(1, 0, 0);
                coord2 = coordS + vec3u(2, 0, 0);
            }
            case 1: {
                coord1 = coordE - vec3u(2, 0, 0);
                coord2 = coordE - vec3u(1, 0, 0);
            }
            case 2: {
                coord1 = coordS + vec3u(1, 0, 0);
                coord2 = coordE - vec3u(1, 0, 0);
            }
            case 3: {
                coord1 = coordS + vec3u(1, 0, 0);
                coord2 = coordS + vec3u(2, 0, 0);
            }
            default: {
                return; // unreachable when shift == 0
            }
        }
    }

    if (coord1.x < srcBoundary.x) {
        mask &= 0xffff00ffu;
        v[1] = textureLoadGeneral(src_tex, coord1, params.mipLevel).r;
    }
    if (coord2.x < srcBoundary.x) {
        mask &= 0xff00ffffu;
        v[2] = textureLoadGeneral(src_tex, coord2, params.mipLevel).r;
    }

    let readDstBufAtMid: bool = (params.srcExtent.x + params.shift > params.bytesPerRow)
        && (params.srcExtent.x < params.bytesPerRow);
    if (readDstBufAtMid && id.x == 0) {
        let original: u32 = dst_buf[dstOffset];
        result = (original & mask) | (encodeVectorInU32General(v) & ~mask);
    } else {
        result = encodeVectorInU32General(v);
    }
}